Personal breathalyzer having digital circuitry

ABSTRACT

The present invention relates to a portable, personal breath tester device for testing the blood alcohol content of the user of the device. The breath tester comprises a circuit board, wherein a sensor, a liquid crystal display, and a processing unit are installed on and electrically connected to the circuit board. The processing unit receives a voltage signal from the sensor representing the blood alcohol content of the user and converts the voltage signal to a precise value that is displayed on the liquid crystal display.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a divisional of prior application U.S. Ser.No. 11/745,854 filed May 8, 2007, now U.S. Pat. No. 7,797,892, whichclaims the benefit of U.S. Provisional Patent Application No.60/746,716, filed on May 8, 2006.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates the gaseous breath detection devices, andmethods for using the same, and more particularly to a portable personalgaseous breath detection device incorporating digital circuitry toanalyze a sample of alveolar air from the user of the device for thepresence of alcohol.

2. Background Art

The present invention relates generally to devices and methods fordetermining the concentration of alcohol in a mixture of gases and moreparticularly, the invention relates to a device and method fordetermining the concentration of alcohol in a breath sample forapplication in sobriety detection systems.

Various techniques have been employed for calculating a person's bloodalcohol concentration by measuring breath samples. A first methodemploys an infrared absorption technique for determining the bloodalcohol concentration. Breath alcohol levels are measured by passing anarrow band of IR light, selected for its absorption by alcohol, throughone side of a breath sample chamber and detecting emergent light on theother side. The alcohol concentration is then determined by using thewell-known Lambert-Beers law, which defines the relationship betweenconcentration and IR absorption. This IR technology has the advantage ofmaking real-time measurements; however, it is particularly difficult andexpensive to achieve specificity and accuracy at low breath alcoholconcentration levels. Also, the IR detector output is nonlinear withrespect to alcohol concentration and must be corrected by measurementcircuits.

A second method employs a fuel cell together with an electronic circuit.In breath alcohol testing devices presently used commercially, in whichfuel cells are employed, the conventional way of determining breathalcohol is to measure a peak voltage across a resistor due to the flowof electrons obtained from the oxidation of breath alcohol on thesurface of the fuel cell. Although this method has proven to have highaccuracy levels, there are a number of problems. The peaks become lowerwith repeated use of the fuel cell and vary with different temperatures.In order to produce a high peak, it is customary to put across theoutput terminals of the fuel cell a high external resistance, on theorder of a thousand ohms, but the use of such a high resistance producesa voltage curve which goes to the peak and remains on a high plateau foran unacceptably long time. To overcome that problem, fuel cell systemsbegan to short the terminals, which drops the voltage to zero while theshort is across the terminals. However, it is still necessary to let thecell recover, because if the short is removed in less than one-half totwo minutes after the initial peak time, for example, the voltage creepsup. Peak values for the same concentration of alcohol decline withrepeated use whether the terminals are shorted or not, and require 15-25hours to recover to their original values.

In addition, individual fuel cells differ in their characteristics. Allof them slump with repeated use in quick succession and also after a fewhours' time of non-use. They degrade over time, and in the systems usedheretofore, must be re-calibrated frequently. Eventually, they degradeto the place at which they must be replaced. Presently, the cell isreplaced when it peaks too slowly or when the output at the peakdeclines beyond practical re-calibration, or when the background voltagebegins creeping excessively after the short is removed from the cellterminals.

Systems employing this method were also cost prohibitive for manyapplications. One reason for the high cost associated with the fuel celltechniques is that the method requires that the breath sample be of adeterminable volume. Historically, this has been accomplished throughthe use of positive displacement components such as piston-cylinder ordiaphragm mechanisms. The incorporation of such components within anelectronic device necessarily increases the costs associated with thedevice.

In a third method, the alcohol content in a breath sample is measuredusing a semiconductor sensor commonly referred to as a Tagucci cell.Among the advantages of devices utilizing semiconductor sensors aresimplicity of use, light weight, and ease of portability and storage.Such units have been employed in law enforcement work as “screeningunits,” to provide preliminary indications of a blood alcohol contentand for personal use. Although this method provides a low cost device,instruments incorporating this method have proved to have poor accuracybecause of the need to hold input voltage signals to the electroniccomponents of the device at constant, steady, regulated levels.

Accordingly, it is desirable to have a breath test device that is easyto use yet accurate in its results, is portable and is an item that theuser will remember to bring with him/her to an event or location wherealcohol is being consumed.

BRIEF SUMMARY OF THE INVENTION

The present invention provides a electronic breath analyzer. Theelectronic breath analyzer includes a gas sensor for alcohol detection.The gas sensor having a heater and a gas sensing element. A microcontroller including a general control output, a reference value inputand a gas sensing element input. The gas sensing element input iscoupled to the gas sensing element. The micro controller is adapted toprovide an initiate reading and comparison signal at the general controloutput. A reference value register includes a reference value in theregister, and having a read initiate input and a reference value output.A general control module includes a control input, a read registeroutput, and an enable gas sensor output. The control input is coupled tothe general control output, the read register output is coupled to theread initiate input and provides a read initiate signal upon receivingthe initiate reading and comparison signal at the general controlmodule. The enable gas sensor output is coupled to the gas sensor andproduces an enable signal upon receiving the initiate reading andcomparison signal at the general control module.

In one embodiment, the general control module includes an NPN transistorhaving an emitter coupled to VCC, the base coupled to the microcontroller, and the collector is coupled to the sensing element througha resistor, and the collector is also coupled to VCC of a memory chip toenable shifting serial reference data to the micro controller.Concurrently, the micro controller produces a clock signal at the clockinput of the memory chip.

In one embodiment, a first and second stage transistor circuit isprovided to amplify current coupled to the gas sensor.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 shows a block diagram of a breath tester system according to apreferred embodiment of the present invention;

FIGS. 2 a-c show a circuit schematic diagram of a breath tester systemaccording to a preferred embodiment of the present invention;

FIG. 3 shows detailed schematic of the pin configuration of themicroprocessor of a preferred embodiment of the present invention;

FIG. 4 is a table providing details of the pins of the microprocessor ofFIG. 3;

FIGS. 5 a-c show graphical representations of output waveforms ofvoltage (vertical axis) over time (horizontal axis) of electricalcomponents of a preferred embodiment of the present invention;

FIG. 6 shows a flow diagram of a breath tester system according to apreferred embodiment of the present invention in operation;

FIG. 7 shows a flow diagram of the steps of calibrating the breathtester of the present invention;

FIGS. 8 a-b show a circuit schematic diagram of a breath tester systemaccording to a second preferred embodiment of the present invention;

FIG. 9 shows a detailed schematic of the pin configuration of themicroprocessor of a preferred embodiment of the present invention;

FIGS. 10 a-10 b are tables providing details of the pins of themicroprocessor of FIG. 9; and

FIG. 11 is a block diagram of the microprocessor of a preferredembodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1 and 2 show a breath tester device 10 in accordance with a firstpreferred embodiment of the present invention for testing a breathsample from the user of the device and calculating the blood alcoholcontent of the breath sample. As is seen in the block diagram of FIG. 1and the circuit schematic of FIG. 2, the breath tester 10 comprises thefollowing modules: Processor Module 12; Crystal Module 14; Switch Module16; Power Module 18; Sensor Preheat Module 20; Sensor Module 22; GeneralControl Module 24; Look-Up Reference Module 26; Display Module 28; andReset Module 30. The individual modules have been organized and namedfor purposes of convenience in describing the structure and arrangementof components in this preferred embodiment and should not be consideredas limiting in any manner.

As is seen in FIG. 1, the Processor Module 12 is central to andelectrically coupled to the remaining modules. In addition, the PowerModule 18 is also coupled to the Sensor Preheat Module 20. The SensorPreheat Module 20 is in turn coupled to the Sensor Module 22. The SensorModule 22 is coupled to the General Control Module 24, which is coupledto the Look-Up Reference Module 26.

The circuit elements of the modules shown in FIG. 1 will now bedescribed in greater detail. The Processor Module 12 is composed of amicroprocessor chip 32 and programming unit 34. In a preferredembodiment of the present invention, the microprocessor 32 comprises an8-bit RISC type chip with low power, high speed CMOS technology andhaving 16K×13 bits of internal memory. The microprocessor 32 furthercomprises an on-chip watchdog timer, program ROM, data RAM, LCD driver,programmable real time clock/counter, internal interrupt, power downmode, built-in three-wire SPI, dual PWM (Pulse Width Modulation),6-channel 10 bit A/D converter, and tri-state I/O. FIG. 3 shows the pinconfiguration of microprocessor 32 in detail and FIG. 4 shows a tableproviding additional description of each pin on the microprocessor 32.The microprocessor 32 used in a preferred embodiment of the presentinvention is manufactured by Elan Microelectronics Corp. and is sold asProduct No. eFH5830AD. However, any suitable microprocessor can beutilized for purposes of the present invention.

Referring to the operation of the Switch Module 16 and Power Module 18(as shown in FIG. 2 c), depressing the switch 36 will ground thepositive terminal of the power source 38 causing a voltage to flow alongthe established pathway. The emitter end of the transistor 40 is coupleddirectly to the positive terminal of power source 38 and thereforereceives voltage Vb from the power source 38. The base of the transistor40 is also coupled to the positive terminal of power source 38 acrossresistor 42. Accordingly the base end of transistor 40 receives avoltage of Vb minus the voltage drop across resistor 42. Becausetransistor 40 is in a P-N-P configuration and the voltage at the base isless than the voltage at the emitter, the transistor is biased closed,coupling the emitter and collector of transistor 40 and enabling Vbminus the voltage drop across transistor 40 to flow towards the step-upconverter 44.

The step-up converter 44, steps up the input voltage signal to a voltageof +5V. In another preferred embodiment of the present invention, shownin FIG. 8 b and described in detail below, the step-up converter 44steps up the input voltage signal to a voltage of +4V. The +5V voltagesignal generated by the Power Module 18 is coupled to the components ofthe Processor Module 12 via the AVDD power pin (Port 7), the GeneralControl Module 24, the Look-Up Reference Module 26, and the Reset Module30. Voltage Vb from the power source 38 is coupled to the Sensor PreheatModule 20. In a preferred embodiment of the present invention thestep-up converter 44 is a PFM controlled, step-up DCIDC convertermanufactured by Torex Semiconductor and is sold under Product NumberXC6382. The power source in this embodiment of the present invention isa 3V DC battery.

The Switch Module 16 (shown in FIG. 2 c) also comprises an “electronic”switch that, when triggered, will enable the power source 38 to providevoltage to the device 10 if the user of the device releases the switch36. The base of transistor 76 is coupled to the PC3 input/output pin(Port 33) of microprocessor 32. Once powered up, the microprocessor 32generates and sends an output voltage signal to the base of thetransistor 76. Because transistor 76 is configured in the N-P-Nconfiguration and the emitter is coupled to ground, the output voltagesignal causes the transistor 76 to be biased closed, coupling theemitter and collector. Because the collector of transistor 76 is coupledto the base of the transistor 40, transistor 76 serves as an electronicswitch, keeping transistor 40 biased closed to enable Vb from thepositive terminal of power source 38 to supply a voltage to the SensorPreheat Module 20 and the step-up converter 44. When the switch 36 isreleased and the microprocessor 32 terminates the power signal sent tothe base of the base of transistor 76, then the power source 38 will nolonger provide voltage to the components of the device 10. Themicroprocessor 32 includes an automatic shut-off routine that terminatesthe power signal sent to the base of the transistor 76 after a presetterm of inactivity.

Turning to the Reset Module 30 (shown in FIG. 2 c), the emitter oftransistor 46 is coupled directly to the +5V voltage signal from thestep-up converter 44 of the Power Module 18. The voltage at the base ofthe transistor 46 comprises the +5V voltage signal from the step-upconverter 44 minus the voltage drop across resistor 48. Becausetransistor 46 is in a P-N-P configuration, the transistor 46 is biasedclosed, coupling the emitter and collector and sending an input signalto the RESET pin (Port 21) of microprocessor 32 causing the breathtester circuit to reset itself and prepare to take a new reading.

Turning to the Sensor Preheat Module 20 (shown in FIG. 2 b), at one endof the module 20, the emitter of transistor 50 is coupled directly tothe positive terminal of power source 38 and, therefore, has a voltageof Vb. The second end of the Sensor Preheat Module 20 is coupled to thePCIIPWMI pin (Port 31) of the microprocessor 32 and receives a powersignal from the microprocessor 32. The breath tester circuit utilizesthe pulse width modulation function of the microprocessor 32 to controltransistors 50 and 52 of the Sensor Preheat Module 20 and provide to theSensor Module 22 constant voltage with a high current. The transistor 52is configured in the N-P-N configuration with the emitter coupled toground. Accordingly, providing a positive voltage signal to the base oftransistor 52 will bias the transistor 52 closed, coupling the base oftransistor 52 to ground. The base of transistor 50 is also coupled tothe collector of transistor 52 and is therefore responsive to thevoltage signal at the collector of transistor 52. As is seen in thewaveform diagrams of FIGS. 5 a-5 c, when the microprocessor 32 providesa pulse voltage signal to the Sensor Preheat Module 20 through thePCIIPWMI pin, the transistor 52 is biased closed and the voltage at thecollector is coupled to ground. Because the transistor 50 is in a PN-Pconfiguration, when the voltage at the base of transistor 50 is coupledto ground via transistor 52, the transistor 50 is biased closed,coupling the emitter and collector and providing a steady voltage to theSensor Module 22. The Pulse Width Modulation signal sent by themicroprocessor 32 controls the operation of transistors 50 and 52 toprovide a 0.9V equivalent DC voltage to the Sensor Module 22.

In a preferred embodiment of the present invention, the Sensor Module 22comprises a tin dioxide semiconductor gas sensor 54. Tin dioxide sensorshave high sensitivity to the presence of alcohol, however, it iscontemplated that other suitable gas sensors are available and can beutilized in the present invention. The sensor 54 comprises a heatingelement 56 and a sensor element 58. The heating element 56 comprises aresistor having a first end coupled to the voltage output of the SensorPreheat Module 20 and a second end coupled to ground. The sensingelement 58 comprises a variable resistor having a conductivity thatvaries depending on the temperature of the sensor and the concentrationof alcohol vapors present. A tin dioxide gas sensor manufactured by FiS,Inc. of Japan and is sold under Product Number SB-30 is utilized in thispreferred embodiment of the present invention.

In order to obtain optimum performance from the sensor 54 the voltageapplied across the heating element 56 must be held steady. The sensor 54of the present invention exhibits optimum performance when a voltage of0.9V is applied to the heating element 56. As previously described, thecomponents of the Sensor Preheat Module 20 are selected to provide aconstant 0.9V to the heating element during operation of the breath testdevice 10 of the present invention. Reference point 60 is coupled tomicroprocessor 32 at AD2/P61 input pin (Port 16) to enable themicroprocessor 32 to monitor the voltage at reference point 60.

The sensing element 58 operates at a circuit voltage of preferably lessthan 5V. The sensor 54 output is also controlled by the transistor 62 ofthe General Control Module 24. The emitter of transistor 62 is coupledto the output of the step-up converter 44 of the Power Module 18 and isat a voltage of 5V. Whereas transistor 62 is configured in a P-N-Pconfiguration, the emitter will be coupled to the collector when the 5Vpower signal is applied to the emitter. By controlling the voltage tothe output terminal of the sensor 54, transistor 62 is controlling theoutput power signal of sensor 54. The output signal representing thevoltage at the sensing element 58 is measured at reference point 66adjacent to load resistor 68 and is coupled to the microprocessor 32 atthe ADI/P60 input pin (Port 17) for monitoring by the microprocessor 32.

The transistor 62 also controls the voltage (Vcc) to the memory 70 ofthe Look-Up Reference Module 26. In a preferred embodiment, the memory70 comprises an electrically erasable and programmable read-only memory(EEPROM) unit having at least 2048 bits of serial memory. An EEPROMsuitable for use in the present invention is manufactured by Atmel Corp.and sold under Product No. AT2402C. The EEPROM 70 is used to storecalibration data and look-up tables utilized by the microprocessor 32during operation of the breath test device 10. EEPROM 70 comprises aplurality of memory locations which serve as individually addressablereference registers containing values for the microprocessor to compareagainst the output of the sensing element during calibration andoperation of the electronic breath analyzer. The EEPROM is coupled tothe base of transistor 62 and operates at a voltage (Vcc) provided byand controlled by transistor 62.

The EEPROM 70 is used to store calibration and look-up table informationused by the microprocessor 32 to calculate the blood alcohol contentfrom the output voltage signal of the sensing element 58. The breathtester device 10 is calibrated prior to use and may be recalibrated withnew calibration and look-up table information being entered at theprogramming unit 34 and stored on the EEPROM 70. Data stored on theEEPROM 70 is clocked out to the microprocessor 32 at Serial Data (SDA)pin in response to receiving clocking input signals from themicroprocessor 32 at the Serial Clock (SCL) pin. The SDA pin of theEEPROM 70 is coupled to the P76/SCK pin (Port 23) of the microprocessor32. The SCL pin of the EEPROM 70 is coupled to the P74/SDI input pin(Port 25) and P75/SDO output pin (Port 24) of the microprocessor 32.

The speed of the microprocessor 32, and in turn the clocking signalgenerated by the microprocessor 32 and received by the EEPROM 70, isdetermined by the oscillation of the crystal 72 of the Crystal Module14. It is contemplated that any suitable crystal can be used in thepresent invention. While in this embodiment of the present invention,the memory 70 is a separate component than the microprocessor 32, it iscontemplated that a microprocessor with sufficient internal memory canbe utilized to perform the same functions as the separate memory andmicroprocessor configuration described herein.

The microprocessor 32 is also coupled to a Display Module 28 (shown inFIG. 2 a). In a preferred embodiment of the present invention, theDisplay Module 28 comprises a liquid crystal display (LCD) 74. Afterperforming the comparison of the data collected at reference point 60against the date stored in EEPROM 70, the microprocessor 32 will causethe appropriate output to be displayed on the LCD 74. The LCD 74 is alsoused to display messages to the user of the device 10, as will bedescribed in detail below.

Referring now to FIG. 6, along with FIGS. 1 and 2, a flow chart showingoperation of the breath test device 10 of the present invention isshown. The first step of operation 76 of the device 10 is to depress theswitch 36 causing the Preheat Sensor Module 20 to warm up the SensorModule 22 to proper operating temperature (78, FIG. 6). While the SensorModule 22 is warming up 78, the microprocessor 32 sends output signalsto the LCD 74 causing the LCD 74 to display a WAIT message 80 to theuser of the device 10. When the Sensor Module 22 is at the properoperating temperature, the microprocessor 32 will send output signals tothe LCD 74 causing the LCD 74 to display a BLOW message 82 to the userof the device 10, indicating to the user that the unit is ready to beused. Next, the user of the device 10 will blow on the Sensor Module 22for three seconds (84, FIG. 6) to ensure that the sensing element 58 isexposed to a sufficient volume of alveolar air to take a proper reading.The Sensor Module 22 generates an output signal that is sent to themicroprocessor 32 for comparison against stored values from the EEPROM70 to determine the alcohol content of the sample of air (86, FIG. 6).Once the comparison and calculation is performed by the microprocessor32, the microprocessor 32 generates and sends the appropriate outputsignals to the LCD 74, causing the LCD 74 to display the calculatedblood alcohol level in units between 0.02% and 0.0%, in increments of0.01% (88, FIG. 6).

If the user of the device 10 desires to have additional readings taken,the user will depress the switch 36 (76, FIG. 6) causing the system toreset for a subsequent reading. If the user does not test subsequentsamples, the microprocessor 32 will automatically shut the device 10 offafter a preset period of time (90, FIG. 6).

FIG. 7 shows a flow diagram of the calibration process of the presentinvention. Referring to FIGS. 2 and 7, calibration begins by jumpershorting 92 the input pin P71 (Port 28) of the microprocessor 32 as afirst point of calibration for 0.02% blood alcohol content. Next 94, theswitch 36 is depressed to provide power to the device 10. The SensorModule 22 is preheated 96 for one to fifteen seconds, dependant on thelast time the device 10 was used. Once the Sensor Module 22 ispreheated, a mixing solution is prepared with distilled water andethanol to a represent a known blood alcohol content. In the presentexample, the mixing solution is prepared to represent a 0.02% bloodalcohol content and is sprayed 98 on the Sensor Module. Themicroprocessor 32 is then calibrated with the 0.02% blood alcoholcontent data 100. If the device is not to be calibrated for 0.08% bloodalcohol content (decision 102), the calibration process is complete, andthe process ends 114.

Otherwise, when the device 10 is to be calibrated for 0.08% bloodalcohol content as well, input pin P72 (Port 27) of the microprocessor32 is jumper shorted at a second point 104. Next 106, the switch 36 isdepressed to provide power to the device 10. The Sensor Module 22 isagain preheated 108 for one to fifteen seconds, dependant on the lasttime the device 10 was used. However the preheat period should berelatively short because the device 10 was recently preheated forcalibration of 0.02% blood alcohol content. Once the Sensor Module 22 ispreheated, a mixing solution is prepared with distilled water andethanol to a represent a 0.08% blood alcohol content and is sprayed 110on the Sensor Module. The microprocessor 32 is then calibrated with the0.08% blood alcohol content data 112 and the calibration process iscomplete 114.

Referring to FIGS. 8 a-b, a second preferred embodiment of the presentinvention is shown. The same reference numbers corresponding to similarcircuit modules and circuit elements present in all preferredembodiments of the invention described herein will be utilized todescribe the present preferred embodiment. As is seen in the circuitschematic of FIGS. 8 a-b, the breath tester 10 comprises the followingmodules: Processor Module 12; Crystal Module 14; Switch Module 16; PowerModule 18; Sensor Preheat Module 20; Sensor Module 22; Look-Up ReferenceModule 26; Display Module 28; and Reset Module 30. The individualmodules have been organized and named for purposes of convenience indescribing the structure and arrangement of components in a preferredembodiment and should not be considered as limiting in any manner.

The Processor Module 12 is composed of a microprocessor chip 32. In apreferred embodiment of the present invention, the microprocessor 32comprises an 8-bit chip with low power, high speed CMOS technology andhaving LCD controller/driver and pulse width modulation features. FIG. 9shows the pin configuration of microprocessor 32 in detail and FIGS. 10a-10 b show tables providing additional description of each pin on themicroprocessor 32. FIG. 11 provides additional details of themicroprocessor 32. The microprocessor 32 used in this preferredembodiment of the present invention is manufactured by SamsungElectronics Co., Ltd. and is sold as Product No. S3P9228. However, anysuitable microprocessor can be utilized for purposes of the presentinvention.

Referring to the operation of the Switch Module 16 and Power Module 18(shown in FIG. 8 b), depressing the switch 36 will ground the positiveterminal of the power source 38 causing a voltage to flow along theestablished pathway. The emitter end of the transistor 40 is coupleddirectly to the positive terminal of power source 38 and thereforereceives voltage Vb from the power source 38. The base of the transistor40 is coupled to the positive terminal of power source 38 acrossresistor 42. Accordingly the base end of transistor 40 receives avoltage of Vb minus the voltage drop across resistor 42. Becausetransistor 40 is in a P-N-P configuration and the voltage at the base isless than the voltage at the emitter, the transistor is biased closed,coupling the emitter and collector of transistor 40 and enabling Vbminus the voltage drop across transistor 40 to flow towards the step-upconverter 44.

The step-up converter 44, steps up the input voltage signal to a voltageof +4V. The +4V voltage signal generated by the Power Module 18 iscoupled to the components of the Processor Module 12 via the VDD powerpin (Port 5), the Look-Up Reference Module 26, and the Reset Module 30.Voltage Vb from the power source 38 is coupled to the Sensor PreheatModule 20. In a preferred embodiment of the present invention thestep-up converter 44 is a PFM controlled, step-up DCIDC convertermanufactured by Torex Semiconductor and is sold under product numberXC6382. The power source 3 is in this embodiment of the presentinvention two 1.5V DC batteries.

The Switch Module 16 also comprises an “electronic” switch that, whentriggered, will enable the power source 38 to provide voltage to thedevice 10 if the user of the device releases the switch 36. The base oftransistor 76 is coupled to the P0.2 input/output pin (Port 41) ofmicroprocessor 32. Once powered up, the microprocessor 32 generates andsends an output voltage signal to the base of the transistor 76. Becausetransistor 76 is configured in the N-P-N configuration and the emitteris coupled to ground, the output voltage signal causes the transistor 76to be biased closed, coupling the emitter and collector. Because thecollector of transistor 76 is coupled to the base of the transistor 40,transistor 76 serves as an electronic switch, keeping transistor 40biased closed to enable Vb from the positive terminal of power source 38to supply a voltage to the Sensor Preheat Module 20 and the step-upconverter 44. When the switch 36 is released and the microprocessor 32terminates the power signal sent to the base of the base of transistor76, then the power source 38 will not provide voltage to the componentsof the breath test device 10. The microprocessor 32 includes anautomatic shut-off routine that terminates the power signal sent to thebase of the transistor 76 after a preset period of inactivity.

Turning to the Reset Module 30 (shown in FIG. 8 a), the emitter oftransistor 46 is coupled directly to the +4 V voltage signal from thestep-up converter 44 of the Power Module 18. The voltage at the base ofthe transistor 46 comprises the +4V voltage signal from the step-upconverter 44 minus the voltage drop across resistor 48. Becausetransistor 46 is in a P-N-P configuration, the transistor 46 is biasedclosed, coupling the emitter and collector and sending an input signalto the RESET pin (Port 12) of microprocessor 32 causing the breathtester circuit to reset itself and prepare to take a new reading.Turning to the Sensor Preheat Module 20 (shown in FIG. 8 b), at one endof the module 20, the emitter of transistor 50 is coupled directly tothe positive terminal of power source 38 and, therefore, has a voltageof Vb. The second end of the Sensor Preheat Module 20 is coupled to theP0.1 input/output pin (Port 1) of the microprocessor 32 and receives apulsed power signal from the microprocessor 32. The breath testercircuit utilizes the pulse width modulation capability of themicroprocessor 32 to control transistors 50 and 52 of the Sensor PreheatModule 20 and provide to the Sensor Module constant voltage with a highcurrent. The transistor 52 is configured in the N-P-N configuration withthe emitter coupled to ground. Accordingly, providing a positive voltagesignal to the base of transistor 52 will bias the transistor 52 closed,coupling the base of transistor 52 to ground.

Turning to the Sensor Preheat Module 20, at one end of the module 20,the emitter of transistor 50 is coupled directly to the positiveterminal of power source 36 and, therefore, has a voltage of Vb. Thesecond end of the Sensor Preheat Module 20 is coupled to the P0.1input/output pin (Port 12) of the microprocessor 32 and receives apulsed power signal from the microprocessor 32. The breath testercircuit utilizes the pulse width modulation capability of themicroprocessor 32 to control transistors 50 and 52 of the Sensor PreheatModule 20 and provide to the Sensor Module constant voltage with a highcurrent. The transistor 52 is configured in the N-P-N configuration withthe emitter coupled to ground. Accordingly, providing a positive voltagesignal to the base of transistor 52 will bias the transistor 52 closed,coupling the base of transistor 52 to ground.

The base of transistor 50 is also coupled to the collector of transistor52 and is therefore responsive to the voltage signal at the collector oftransistor 52. As is seen in the waveform diagrams of FIGS. 5 a-5 c,when the microprocessor 32 provides a pulse voltage signal to the SensorPreheat Module 20 through the P0.1 pin, the transistor 52 is biasedclosed and the voltage at the collector is coupled to ground. Becausethe transistor 50 is in a P-N-P configuration, when the voltage at thebase of transistor 50 is coupled to ground via transistor 52, thetransistor 50 is biased closed, coupling the emitter and collector andproviding a steady voltage to the Sensor Module 22. The pulsed outputsignal sent by the microprocessor 32 controls the operation oftransistors 50 and 52 to provide a 0.9V equivalent DC voltage to theSensor Module 22.

In a preferred embodiment of the present invention, the Sensor Module 22comprises a tin dioxide semiconductor gas sensor 54. Tin dioxide sensorshave high sensitivity to the presence of alcohol, however, it iscontemplated that other suitable gas sensors are available and can beutilized in the present invention. The sensor 54 comprises a heatingelement 56 and a sensor element 58. The heating element 56 comprises aresistor having a first end coupled to the voltage output of the SensorPreheat Module 20 and a second end coupled to ground. The sensingelement 58 comprises a variable resistor having a conductivity thatvaries depending on the temperature of the sensor and the concentrationof alcohol vapors present. A tin dioxide gas sensor manufactured by FiS,Inc. of Japan and sold as Product No. SB-30 is utilized in a preferredembodiment of the present invention.

In order to obtain optimum performance from the sensor 54 the voltageapplied across the heating element 56 must be held steady. The sensor 54of the present invention exhibits optimum performance when a voltage of0.9V is applied to the heating element 56. As previously described, thecomponents of the Sensor Preheat Module 20 are selected to provide aconstant 0.9V to the heating element during operation of the breath testdevice 10 of the present invention. Reference point 60 is coupled tomicroprocessor 32 at P1.2/AD2/INT input/output pin (Port 3) to enablethe microprocessor 32 to monitor the voltage at reference point 60. Theoutput signal representing the voltage at the sensing element 58 ismeasured at reference point 66 adjacent to load resistor 68 and iscoupled to the microprocessor 32 at the P1.0AD0/INT input/output pin(Port 1) for monitoring by the microprocessor 32.

In a preferred embodiment, the memory 70 of the Look-Up Reference Module26 comprises an electrically erasable and programmable read-only memory(EEPROM) unit having at least 2048 bits of serial memory. An EEPROMsuitable for use in the present invention is manufactured by Atmel Corp.and sold under Product No. AT2402C. The EEPROM 70 is used to storecalibration data and look-up tables utilized by the microprocessor 32during operation of the breath test device 10. The EEPROM is coupled to+4V output of the step up voltage converter 44.

The EEPROM 70 is used to store calibration and look-up table informationused by the microprocessor 32 to calculate the blood alcohol contentfrom the output voltage signal of the 20 sensing element 58. The breathtester device 10 is calibrated prior to use and may be recalibrated withnew calibration and look-up table information being entered at theprogramming unit 34 and stored on the EEPROM 70. EEPROM 70 comprises aplurality of memory locations which serve as individually addressablereference registers containing values for the microprocessor to compareagainst the output of the sensing element during calibration andoperation of the electronic breath analyzer. Data stored on the EEPROM70 is clocked out to the microprocessor 32 at Serial Data (SDA) pin inresponse to receiving clocking input signals from the microprocessor 32at the Serial Clock (SCL) pin. The SDA pin of the EEPROM 70 is coupledto the P2.2/S1 pin (Port 14) of the microprocessor 32. The SCL pin ofthe EEPROM 70 is coupled to the P2.3 pin (Port 13) of the microprocessor32. The speed of the microprocessor 32, and in turn the clocking signalgenerated by the microprocessor 32 and received by the EEPROM 70, isdetermined by the oscillation of the crystal 72 of the Crystal Module14. It is contemplated that any suitable crystal can be used in thepresent invention. While in this embodiment of the present invention,the memory 70 is a separate component than the microprocessor 32, it iscontemplated that a microprocessor with sufficient internal memory canbe utilized to perform the same functions as the separate memory andmicroprocessor configuration described herein.

The microprocessor 32 is also coupled to a Display Module 28. In apreferred embodiment of the present invention, the Display Module 28comprises a liquid crystal display (LCD) 74. After performing thecomparison of the data collected at reference point 60 against the datestored in EEPROM 70, the microprocessor 32 will cause the appropriateoutput to be displayed on the LCD 74. In the present embodiment, the LCD74 displays the numeric value of the blood alcohol content of the userof the device 10. The LCD 74 is also used to display messages to theuser of the device 10.

The circuit elements and arrangement described herein enables the breathtester device 10 of the present invention to address the need for asmall, simple to use and convenient breath tester device. The circuitrycan be packaged in a small housing to enable the breath tester to beextremely portable, such as a small attachment to key chain. Theincorporation of the LCD results in the device conveying simple andclear instructions to the user of the device and simple and cleardisplay of blood alcohol content. In addition, the selection of thespecific electrical components described herein results in a system thatworks with minimal power requirements, prolonging the life of the powersource and adding further to convenience of operation of the presentdevice.

The foregoing description of an exemplary embodiment has been presentedfor purposes of illustration and description. It is not limited to beexhaustive nor to limit the invention to the precise form disclosed.Obvious modifications or variations are possible in light of the aboveteachings. The embodiment described herein best illustrates theprinciples of the invention and its practical application to therebyenable one of ordinary skill in the art to best utilize the invention invarious embodiments and with various modifications as are suited to theparticular use contemplated. It is intended that the scope of theinvention be defined by the claims appended hereto.

The invention claimed is:
 1. An electronic breath analyzer comprising: agas sensor for alcohol detection, the gas sensor having a heater and agas sensing element; a micro controller including a heater controloutput, the micro controller adapted to provide a heater signal at theheater control output; a gas sensor heater circuit coupled to the gassensor, the gas sensor heater circuit including a first stage transistorcircuit and a second stage transistor circuit, the first stagetransistor circuit having a control input coupled to the heater controloutput of the micro controller, and an output, the second stagetransistor circuit having a control input coupled to the output of thefirst stage transistor circuit, and an output coupled to the heater ofthe gas sensor.
 2. The electronic breath analyzer of claim 1, whereinthe first stage transistor circuit includes an NPN transistor and secondstage transistor circuit includes a PNP transistor, the NPN transistorhaving a base coupled to the heater control output of the microcontroller, an emitter coupled to ground and a collector connected tothe base of the PNP transistor, the PNP transistor having a base coupledto the collector of the first stage transistor circuit, an emittercoupled to a voltage V_(B), and a collector coupled to the heater of thegas sensor.
 3. The electronic breath analyzer of claim 2, wherein afirst resistor (R9) is coupled between the heater control output and thebase of the first stage transistor circuit, a second resistor (R11) iscoupled between the base and emitter of the first stage transistorcircuit, a third resister (R1) is coupled between the output of thefirst stage transistor circuit and the input of the second stagetransistor circuit, and a fourth resistor (R10) is coupled between thebase and emitter of the second stage transistor circuit.
 4. Theelectronic breath analyzer of claim 3, wherein first resistor (R9) is a4.7K ohm resistor, second resistor (R11) is a 100K ohm resistor, thirdresister (R1) is a 270 ohm resistor, and fourth resistor (R10) is a 100Kohm resistor.
 5. The electronic breath analyzer of claim 3, whereinfirst resistor (R9) is a 1K Ohm resistor, second resistor (R11) is a100K Ohm resistor, third resister (R1) is a 270 ohm resistor, and fourthresistor (R10) is a 100K OHM resistor.